1. Field of the Invention
This invention pertains to polyolefins with improved impact strength, obtained by the addition of core-shell polymers compatibilized to the polyolefin matrix via the addition of a polyolefin-acrylic graft copolymer.
2. Description of Related Art
Polyolefins are widely used as general purpose resins, however, from the perspective of practical physical properties, suffer from having low impact strength.
Core-shell polymers are known as useful additives for certain plastics, providing both processing and end use benefits. As processing additives the core-shell polymers allow the melt to be processed more quickly and with better consistency by improving the melting and increasing the melt strength. As performance additives the core-shell polymers increase the impact strength of plastics.
However, it has not been possible to use core-shell polymers in polyolefins since the polyolefins are non-polar and are, therefore, non-compatible with the polar core-shell polymers.
U.S. patent application Ser. No. 315,501, now U.S. Pat. No. 4,957,974 of common ownership herewith, describes the preparation of novel grafted copolymers capable of imparting to polyolefins when blended therewith high tensile modulus and high sag resistance. The graft copolymers of this disclosure are polyolefins having a relatively high weight average molecular weight methacrylate polymer grafted thereto.
Fayt and Teyssie in Polymer Engineering and Science, April 1989, Volume 29, Number 8, pages 538 to 542, disclosed the emulsifying activity of a copolymer of poly (hydrogenated butadiene-.beta.-methyl methacrylate) as an emulsifier for blends of low density polyethylene and polystyrene coacrylonitrile resins.
U.S. Pat. No. 4,430,477 discloses high impact polypropylene compositions comprising polypropylene and a chlorinated polyolefin having styrene graft polymerized thereon.
U.S. Pat. No. 4,156,703 discloses the blending of a polyolefin, namely polyethylene with an acrylic polymer to form a heterogeneous mixture, which has improved processing characteristics.
U.S. Pat. No. 4,180,494 discloses a core-shell polymer comprising about 25 to 95% by weight of an aromatic polyester, about 1 to 8% by weight of an aromatic polycarbonate, and a balance to make 100% of the core-shell polymer having a butadiene based core.
U.S. Pat. No. 4,443,585 discloses polymer impact modifiers used especially for PVC. The impact modifiers of this disclosure are comprised of an olefin and an acrylic copolymer.
U.S. Pat. No. 3,808,180 discloses modified rigid acrylic thermoplastic resin comprising at least 50 weight percent alkyl or aralkyl acrylate, crosslinking and hydrophilic monomers. These materials may be characterized as soft-core hard-shell polymers.
U.S. Pat. No. 3,793,402 discloses an impact resistant thermoformable composition comprising a blend of a thermoplastic polymer and a hard-soft-hard core additive.
U.S. Pat. No. 4,617,329 discloses a core-shell polymer wherein the core is polymerized from a styrenic monomer. The second stage comprises a polymeric soft stage with a rigid thermal plastic outer stage.
The disclosures of the foregoing patents and publications are incorporated by reference herein. It is the object of this invention to incorporate the core-shell polymers as described above into polyolefins.